Thermally responsive switch adapted to function as a high limit switch or as a fan switch with a fixed adjustable temperature differential



June 8, 1965 H. L. RANDOLPH 3,133,433 THERMALLY RESPONSIVE SWITCH ADAPTED To FUNCTION AS A HIGH LIMIT SWITCH OR AS A FAN SWITCH WITH A FIXED ADJUSTABLE TEMPERATURE DIFFERENTIAL 4 Sheets-Sheet 1 Filed Jan. 23, 1962 INVEN TOR. HOLLIS LEE RANDOLPH June 8, 1965 H. RANDOLPH THERMALLY RESPONSIVE SWITCH ADAPTED TO FUNCTION AS A HIGH 1 LIMIT SWITCH OR AS A FAN SWITCH WITH A FIXED ADJUSTABLE TEMPERATURE DIFFERENTIAL Filed Jan. 25, 1962 4 Sheets-Sheet 2 FIG. 4 H045 IN V EN TOR. HOLLIS LEE RANDOLPH ZJZ 14,4 1 K A TTORNE Y6.

June 8, 1965 H. 1.. RANDOLPH 3,188,433 THERMALLY RESPONSIVE SWITCH ADAPTED TO FUNCTION AS A HIGH LIMIT SWITCH OR AS A FAN SWITCH WITH A FIXED ADJUSTABLE TEMPERATURE DIFFERENTIAL 4 Sheets-Sheet 3 Filed Jan. 23, 1962 INVENTOR. HOLLIS LEE RANDOLPH g BY 1" hind, 6a r A TTORNE Y5.

June 8, 1965 H RAND 3,188,433

OLPH THERMALLY RESPONSIVE ITCH ADA D TO FUNCTION AS A HIGH LIMIT SWITC OR AS A F SWITCH WITH A FIXED ADJUSTABLE TEMPERATURE DIFFERENTIAL 4 Sheets-Sheet 4 Filed Jan. 23 1962 "IIIIIIHA'II INVENTOR. HOLLIS LEE RANDOLPH hill, 2444a,

ATTORNEYS.

- proved snap actuating mechanism.

close the contacts.

United States Patent THERMALLY RESPONSIVE SWITCH ADAPTED T0 FUNCTION AS A HIGH Lift/ET SWHC'CHOR AS A FAN SWITCH WITH A FIXED ADJUSTABLE TEMPERATURE DIFFERENTIAL Hollis Lee Randolph, Lakewood, Calii, assignor to Robertshaw Controls Company, Richmond, Va., a corporation of Delaware Filed Jan. 23, 1962, Ser. No. 168,044 13 Claims. (Cl. Nil-138) ment, the contacts open to shut oil? the fan. Switches of this type may also be employed as high limit controls; the switch responding to excessive temperature to break the circuit and cause an electrically operated fuel control valve to close and shut down the system. a

It is an object of this invention to provide a thermally responsive switch which may be utilized as either a fan switch with a fixed temperature difierential, a fan switch with an adjustable temperature differential, or as a high limit switch.

A further object is to provide a thermally responsive switch having improved adjustment mechanism for varying the operating range of the switch.

Still another object is to provide a switch having im- A further objectis to provide a switch which may be selectively biased to return to either an open or closed position upon removal of external forces.

The objects are achieved by the provision of a switch having a fixed contact and a movable contact, the movable contact being supported by a spring device which is arranged to open and close the contacts with a snap action upon the application of an external force. For actuating the contacts, a pair of levers are mounted in scissors fashion on the spring support with one end 'pivotally engaged with adjustment members. Positioned between the free ends of the levers is a bimetal element which actuates the levers in response to temperature variations to open and Movement of the adjustment members varies the temperature range at which the contacts will open and close. j

For adapting the switch as either a high limit switch or a fixed temperature differential fan switch, an auxiliary spring is provided that can be selectively connected to the spring support to bias the contacts to return to either an open or close position upon removal of the external force applied by the bimetal. In either of these situations, it is necessary to use only one actuating lever and adjustment member.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

sectional view taken on line 2-2 of Patented June 8, 1965 ice line 4-4 of FIG. 2 with the switch contacts illustrated in the open position;

FIG. 5 is a view similar to FIG. 4 with the contacts closed;

FIG. 6 is a sectional view taken on line 6-6 of FIG. 4;

FIG. 7 is an exploded perspective view of the switch mechanism with one wall of the switch casing broken away for clarity;

FIG. 8 is an exploded perspective view of the bimetal housing and base plate;

FIG. 9 is a top plan view of a fan switch with a fixed temperature differential embodying the invention;

FIG. 10 is a bottornview of the switch casing of FIG. 9;

FIG. 11 is a top plan view of an adjustable limit switch embodying the invention, and

FIG. 12 is a bottom view of the switch casing of FIG. 11.

FIGURES 1 through 8 illustrate the device arranged to function as a fan switch with an adjustable temperature differential, that is, the temperatures at which the switch contacts open and close can both be selected by adjusting the position of the actuating mechanism. In FIGURES 1 through 3, a switch casing it is mounted on a base plate 12 of a housing 14. Housing 14 is U-shaped in cross section having side members 16 and 18 and a top wall member 20. Mounted in housing 14 is a cantilevered bimetal element 22. One end of bimetal element 22 is secured to the housing by rivets 2-3 with its free end extending toward base plate 12 and having an actuating tab 24 formed thereon. Housing 14 is positioned in an air duct of a heating system or the plenum of a furnace, and variations in temperature cause bimetal element 22 to deflect to provide actuating force for the switch mechanism. In order that the air or other temperature conducting medium may be distributed evenly about bimetal element 22, openings'lo are provided in the side and top walls of housing 14.

Secured to the inner side of the top wall of casing Ill (FIGURES 4 and 5) is a fixed electrical contact 28. Also secured to the top wall of the casing is a mainspring assembly 3%. Mainspring assembly 38 includes a central portion 32 having a pair of resilient arm members 34 and 36 extending from its ends. Arm members 34 and 36 have their ends secured to the casing. Formed integrally with arm member 34 is a resilient contact lever 38 (FIG. 7) having a movable contact 40 secured adjacent its free end. Snap opening and closing of contacts 2% and 4% is provided by an overcenter spring 42 which has its end mounted between the end of contact lever 38 and the edge of central portion 32 of the mainspring assembly. When central portion 32 of spring 30 is moved to the left as indicated in FIG. 5, overcenter spring 42 causes the end of contact lever 38 to deflect to the right until contact 49 closes against contact 28. Conversely, movement of central portion 32 to the right causes overcenter spring 42 to deflect contact 4th to the left to open the contacts, the position illustrated in FIG. 4. Spring assembly 36 is so designed that when deflected in either direction the biasing forces of arms 34 and 36 are balanced against the force of overcenter spring 42 so that the contacts will remain in either of the positions illustrated in FIGURES 4 and 5 unless central portion 32 is acted upon by an external force.

For transmitting the movement of bimetal element 22 to mainspring 3d, a pair of actuating levers 44 and 46 of insulating material are pivotally mounted by rivet 48 to central portion 32 of spring 30. Actuating levers 44 and 46 are complementarily formed and, as illustrated,

are mounted in scissors fashion on central portion 32.

Actutaing levers 44 and 46 are provided with blades 50 and 52, respectively, in the form of pinchers which extend through a slot in base plate 112 and are disposed on opposite side of tab 24 of bimetal element 22. Projecting upwardly from levers 44 and 46 are handles 54 and 516, respectively, which extend through a slot in the upper wall of casing 10. Pivotally mounted on the top of casing 10 is a pair of adjustment arms 58 and 60 (FIG. 1) which are .apertured at 62 and 64, respectively, and handles 54 and 56 are received in apertures 62 and 6.4. Adjustment arms 58 and so provide an abutment for levers 44 and 46 so that deflection f bimetal element 22 against one of the pincher ends of the levers will cause the lever to pivot about adjustment arm 58 or 60 and, acting through its pivotal connection 48 with central portion 132 of spring 313, will cause the spring assembly toshift either to the left or right to actuate the switch contacts.

:By rotation of adjustment arms 53 and as about their pivots, the temperature range at which the switch contacts will be actuated may be varied. For example, counterclockwise rotation of adjustment arm (FIG. 1) will cause blade 52 to move to the left as viewed in FIG. 3 and thus increase the amount of travel required by bimetal element 22 to actuate lever 44.

Adjustmentarms 58 and as are complementary formed, and are pivotally mounted at the r ends on a common axis at rivet 66. Apertures 62 and 64 are disposed over a slot 68 in the top wall of casing 10, slot 68 being elongated to permit movement of handle portions 54 and 56 upon adjustment of arms 58 and so about their pivotal axes at rivet d6. Adjustment arms 58 and so are of spring material and are biased to engage the top of the casing. Slotted holes 711 and/72 adjacent the ends of arms '58 and 611 respectively, cooperate with raised projections 74 formed on the top outer wall of the casing in an arcuate pattern to maintain the setting .of the adjustment arms under vibration. Also provided adjacent the ends of the adjustment arms is a series of circular depression-s 7 6 which are likewise arranged in an arcuate pattern for receiving pins (not shown) which can be used to provide either a maximum setting with a'single pin, or a fixed setting by insertion of pins on opposite sides of each adjustment arm.

For indicating the temperature setting of the adjustment arms, a dial 78 with apropriate temperature markings is provided on the top wall for cooperation with the pointed ends of the adjustment levers 58 and 60. Dial 718 may be a gum-backed paper dial. Counterclockwise adjustment of adjustment arm '58 which is the oif adjustment as indicated, reduces the temperature at which the switch contacts will open to shut down the fan. Clockwise pivotal adjustment of the on adjustment arm 60 toward the higher temperature setting of the dial increases the temperature at which the switch contacts will close to start the fan into operation.

With reference to FIGURE 7 the switch mechanism and its method of assembly is illustrated in detail. Switch casing is of electrical insulating material and forms a substantially rectangular, open ended cavity having a front wall 80, side walls 62 and 84, rear wall 86 and a top wall #8 8. Side wall '82 is broken away in FIG. 7 to a Xpose the interior of the casing. Projecting from top wall '88 adjacent side wall 84 is .a post 90. Formed in side wall 84 is a vertical groove 92 having a projecting lip 94 for receiving arm member 3 6 of mainspring 130. Projecting from top wall '88 at substantially its longitudinal axis is an insulating rib 96 for elect-rically insulating the mounting plates of the fixed and movable contacts from each other. Holes 98 and 100 are formed in top wall 88 on either side of insulating rib 9 6 for receiving terminal screws and for mounting the contact plates on the casing.

Fixed contact '28 is mounted on an arm member 101 which is rigidly secured to a bracket 102 by a rivet'103. :Bracket 1112 is provided with a mounting plate 104 which is apertured at 1%. Arm member 101 is fixed against rotation by the cooperation of a tab 107 with a notch 107a. Bracket 102 is secured to the casing by a terminal nut 1018 (BIG. 2) which is received in hole 160 and aperture 1%, with its inner end spun over at 110 to clamp plate 104 to the casing. For preventing rotation of bracket 111-2 about nut 110, a lip 112 at the forward end of bracket r1112 cooperates with a slot 114 in top wall 38 of the casing.

Arm member 3-6 of mainspring 30 is offset at 116, and an auxiliary spring arm 118 extends from the end of arm member 3 6 for a purpose to be described below. Arm member 34 is secured to a bracket 1211 having a mounting plate 122. Cooperating holes 124 and 125 in bracket 121i and arm member 34, respectively, receive rivets 126 to secure the parts together. secured to the casing with aterminal nut 128 ('FIG. 1) in the same manner as bracket v1112 and'extends along the length of contact lever 38 to'serve as a stop plate for contact 41) (FIGS. 4 and 5). Slots 42am overcenter spring 42 receive tabs 32a and 38a formed on central portion 32 and contact lever 38, respectively.

Mounting lugs 131i and 132' having holes 151 and 133, respectively formed therein, are integrally formed on the outside of front wall 131 of the casing for receiving fasteners to secure the casing to base plate 12. Formed on the outside of rear wall 86 is aboss'134 having a slot 135 and a groove 13% formed therein. Groove 136 cooperates With a similar groove on base plate 12 for receiving a mounting bolt. integrally formed on the top wall'of casing 111 is a pair of stops 1 3-8 for limiting the outward movement of adjustment arms 58 and 60. Walls 1141) project upwardly from the top wall of the casing to form a pair of cavities, substantially rectangular in shape for receiving terminal screws i142 and 144 in nuts 11% and 128, respectively. Rivet st for mounting adjustment arms =58 and 6t on casing 10 is received in a mounting hole 146 in the top wall of the casing.

Main spring 30 is firmly secured adjacent top wall 8 8 by insertion of the end of arm member 36 into groove 92. Offset portion 116 of arm member 36 cooperates with post to provide a force fit between lip 94 of groove 92 and post 90. As pointed out previously, when main spring '31) is in the position illustrated in FIG. 4 with contacts 28 and 40 open, an external force to the left on central portion 32 is required in order to close the contacts due to the action of over center spring 42. After contacts 28 and 4d are closed as illustrated in FIG. 5, an external force to the right on central portion 32 is required in order to open the contacts. Rib 96 serves to electrically insulate plate 104 from lug 122 of bracket 121).

Referring to FIG. 8, base plate 12 is provided with three depressions 146, each having a slot 147 for receiving tabs 148 of bimetal housing 14 which are bent over. after insertion into slots 147 (FIGS. 2 and 3). Blades 51 and 52 of the actuating levers extend through an elongated slot 150 formed in base plate .12 which is covered by an air stop 152 of nylon or some other flexible material. Air stop 152 is provided with a slit for receiving the blade. For cooperation with slot 135 in boss 134 of the switch casing, a .tab 154 is bent upwardly on base plate 12 for insertion into the slot. Apertured recesses 156 and 158 are formed at the forward end of base plate 12 for cooperation with openings 131 and 133 to receive screws 1611 (FIG. 1) which secure casing 10 to base plate 12. Mountmg grooves 162 and 164 are formed at'the front and rear edges of base plate 12 for mounting the assembly on the wall of a duct or other support. After assembly of main spring 30 and switch contacts 28 and 41) in casing 10, the casing is secured to base plate 12 by inserting tab 154 into slot 135, after which tab 154 is then bent over to hold the switch in place as shown in FIG. 1. Screws Bracket 1:20 is arsenal? arms 58 and 60 are then pivotally fastened to casing by rivet 66. The structure described thus far operated as fan control with an adjustable temperature differential.

After assembly and temperature calibration, bimetal housing 14 is inserted into an appropriate opening in a duct or plenum of a forced air furnace, and base plate 12 is mounted to the duct by fasteners which cooperate with slots 162 and 164. Electrical connection with the fan motor is accomplished by connecting wires from the fan motor in series with the switch by terminal screws 14% and 142.

The electrical circuit through the switch can best be described with reference to FIGS. 4 and 5. Current flows from terminal 140 through bracket 120 to main spring which carries contact 40. Ribs 96 insulate contact 4% from contact 28 when the switch is open as illustratedin Referring to FIG. 3, upon an increase'in temperature bimetal 22 deflects to the left to actuate lever 44 and shift central portion 32 of spring 30 to the left as viewed in FIG. 5, causing over-center spring 42 to close the contacts with a snap action, and the current flows from contact 40 to contact 28 and through bracket 102 to terminal 142. Upon satisfaction of the heating requirement and resultant cooling of bimetal 22, bimetal 22 deflects to-the right as viewed inFIG. 3 and acts on blade '55 of actuating lever 46 to shift central portion 32 of spring 35 back to the position illustrated in FIG. 4 to snap open the contacts, thereby shut-ting ofi the fan.

I Movement of the on adjustment arm 6t) to a higher temperature setting, that is, counterclockwise as viewed in FIG. 1 moves blade 50 of actuating lever 44 to the right as viewed in FIG. 3 requiring a greater amount of deflection of bimetal 2 2 to contact the pincher end of blade 59 which results in a higher fan on temperature setting.

1 Conversely movementof the adjustment arm 60 to a lower temperature setting results in the switch contact being closed with less deflection of bimetal 22 providing a lower fan on setting.

7 tion, to throw the switch to on or off position. This" free movement resultsinthe attaining of an increased fan switch differential depending upon the degree of separation of blades 50 and 52.

For adapting the device to function as a fan switch with a fixed temperature differential, adjustment arm 58 and actuating lever 46 are omitted as illustrated in FIGS. 9 and 10. Auxiliary spring 118 is utilized to provide the actuating force for mainspring 30 in oppositionto force induced by deflection of bimetal element 22. With reference again to FIG. 7, a slot 166 is provided in central portion 32 of mainspring 30 adjacent arm member 36. Auxiliary spring 1 18 is provided with three leaves, 118a, 11815 and 1180. Any or all of leaves 118a, 1181; or 1180 can be inserted into slot 166 as illustrated in FIG. 10, to exert a biasing force to the right on central portion 32 tending to separate contacts 28 and 40, providing a normally opened switch. Upon heating of the bimetal element 22, central pontion 32 is deflected to the left as viewed in FIG. 10 against the bias of auxiliary spring 118,

until overcenter spring 42 causes the contacts to snap 6 closed. As bimetal element 22 deflects in the opposite direction upon cooling, auxiliary spring 118 causes central portion 32 of spring 39 to follow the movement of the bimetal to the right until contacts are opened with a snap action' as illustrated in FIG. 10, thereby providing a fixed minimum fan differential.

FIGS. 11 and 12 illustrate the device as utilized as an adjustable limit switch with the on adjustment arm and actuating lever 44 omitted. Auxiliary spring 118 is .bent to the configuration illustrated in FIG. 12 to exert a biasing force to the left on central portion 32 providing a normally closed switch.

When used as a limit switch as shown in FIGS. 11 and 12, bimetal element 22 is reversed in housing 14 so that upon heating it will deflect in a direction to cause main spring 36 to move to the right, resulting in opening contacts 28 and 49 as the pre-set limit off temperature is reached. Dial 7ST is provided with temperature markings in reversed order from that of dial 78 in FIGS. 1 and 9, to

correspond to the reverse action of bimetal 22.

As previously pointed out, all of the adjustable switches can be converted to maximum setting switches by insertion of stop pins in apertures 76 on the switch casing, or if a fixed setting is desired, adjustment arm 58 and/ or 60 can be confined to a desired fixed setting by locating stop pins on opposite sides of the adjustment arm in apertures 76 after properly positioning the-adjustment arms to the desired setting.

While specific examples of the invention have been illustrated and described, it will be understood that the invention is not confined to the exact construction illustrated, but that the various alterations in construction are possible within the scope of the invention as defined by the appended claims.

What is claimed is:

1. A thermally responsive switch comprising,

a switch casing,

a mainspring mounted in the casing,

a movable contact carried by the mainspring,

a fixed contact in the casing,

a pair of levers pivotally mounted in scissors fashion on the mainspring,

adjustment means on the casing,

' each of the levers having one end rotatably engaged with the adjustment means,

and a thermally responsive movable element connected with the casing,

the free ends of the levers being positioned in the path of movement of thethermally responsive element for moving the movable contact into and out of engagement with the fixed contact in response to temperature changes.

2. A thermally responsive switch comprising,

a switch casing,

a mainspring mounted on one wall of the casing,

a resilient-arm member on the mainspring,

a movable contact carried by the resilient arm member,

an overcenter spring connected with the arm member and the mainspring for causing movement of the movable contact in one direction with a snap action upon movement of the mainspring inthe opposite direction,

a fixed contact in the casing,

a pair of levers mounted in scissors fashion on the mainspring,

adjustable stop means on the casing,

one end of each of the levers engaged with the stop means for pivotal movement relative to the stop means,

an actuating element connected with the casing and movable in response to temperature changes,

and the free ends of said levers being disposed on opposite sides of the actuating element in the path of movement thereof for opening and closing said contacts in response to temperature variations.

arse tea Z 3. A thermally responsive switch comprising, a switch casing, I a mainspring including, a central portion,

an arm member 'extendingfrom each end of the central portion, 1

each arm member having its end fixedly mounted and an actuating element connected withthe central portion for moving the central portion in' response to temperature variations to actuate the contacts. 4. A thermally responsive switch as defined in claim further including, abutment means on the casing, a pair of oppositely formed levers mounted in scissors fashion on the central portion of the main'spr'ing,

each of the levers having one end rotatably engaged with the abutment means, the levers having free ends disposed on opposite sides of the actuating element in the path of movement thereof, a said actuating means operative for moving the free end of one of the levers in a direction to close the contacts upon a decrease in temperature, and opperative for moving the free end of the other of the leversin a direction to open 'the'contacts upon an increase in temperature. 5. A thermally responsive switch as defined in claim 4 further including, I v A means for adjusting the position of said abutment means for varying the temperature response of said levers. 6. A thermally responsive switch as defined in claim 3 further including,

an auxiliary spring arm formed on the other of the arm members of the ma-inspring,

the auxiliary spring arm having a free end selectively engageablewith the central portion of the mainspring to resiliently bias the contacts either open or closed,

and said actuating element being operatively connected to move the central portion against the bias of the auxiliary spring in response to temperature variations.

7. A thermally responsive switch as defined in claim further including,

abutment means on the casing, A

a lever pivotally mounted intermediate its end on the central portion of themainspring,

said lever having ,one'endrotatably engaged with the abutment means and its other end disposed in the path of movement of the actuating element,

an auxiliary spring selectively engageable with the central portion of the mainspring to bias the contacts c osed,

and said actuating element being operative to engage the free end of the lever and move the central portion in a direction to open the contacts in response to an increase in temperature.

8. A thermally responsive switch comprising,

a casing having side walls and a top wall,

a slot in the top wall,

a pair of adjustment arms pivotally mounted on the top wall,

' each of the adjustment arms having an aperture radially displaced from the pivotal axis of the arms for cog operating with the slot upon pivotal movement of the arms, I a mainspring having a central portion and a pair of arm members extending from the central portion, said arm members having their ends mounted 'on the opposite side of the top Wall from the adjustrnent levers, i a movable contact carried by one of said arm members, a fixed contact mounted in the casing in the path of movement of the movable contact, a pair of oppositely formed actuating levers pivotally mounted in scissors fashion on'the central portion of the mainspring, each of the actuating levers having one .end'received in an aperture of one of the adjustment arms, the actuating levers havingfree ends disposed in opposed relationship on theopposite side of the central portion from said one .end, I an actuating element having a portion movable in re sponse to variations in temperature, said movable portion being disposed between the free ends of the levers for actuating one of the levers in response'to a preset low temperature to. close the contacts, and actuating the other of the levers in response to a: preset high temperature to open the contacts, a said adjustment arms being selectively positionabl about their pivotal axes to very the range between the high and low temperatures. j 9. A thermally responsive switchcomprising,

a casing having side walls and a top wall, 1 V

a pair of adjustment arms pivotally mounted on the top wall, 1 f

each of the adjustment arms having an aperture formed therein spaced from its pivotal axis,

a fixed contact and a movable contact in the casing,

movable support means .for'themovable contact,

a pair of actuating levers pivotally mountedin scissors fashion intermediate their ends on the movable sup port means,

each of the actuating levers having one end received in the aperture of one of the adjustment arms and a free end disposed in opposed relationship to the free end of the other actuating lever,

and a thermally responsive actuating element disposed between the free ends of the actuating levers and operative in response to decreases in temperature'to pivotally actuate one of the actuating levers about said aperture to close the contacts, and operative, in response to increases in temperature to pivotally rotate the other of the actuating levers about the apertured adjustment arm to open the contacts.

10. A thermally responsive switch as defined in claim 9 including,

a plurality of raised projections arranged in an arcuate pattern on the top wall of the casing in the path of movement of the adjustment arms,

said adjustment arms being resiliently biased toward the top wall and selectively engageable with the projections for restraining the adjustment arms against rotation.

11. A snap acting switch comprising,

a casing, I

a main spring in the casing'including,

a central portion, a pair of resilient arm members integrally formed with the central portion,

one of the arm members extending from one end of the central portion with its end secured to the casing, the other of the arm members extending from the other end of the central portion with its end secured to thecasing, 7 a fixed contact in the casing, a resilient contact lever formed integrally on said one arm member having a free end extending toward the control portion,

a movable contact carried by said contact lever movable into and out of engagement with the fixed contact,

an overcenter spring mounted between said one end of the central portion and the free end of the contact lever,

and means for moving the central portion laterally with respect to the ends of the arm members in response to temperature changes to open and close the contacts with a snap action.

12. A thermally responsive switch as defined in claim 11 including,

an offset portion on the other of the arm members,

an auxiliary spring arm integrally formed on the oilset portion extending substantially parallel to said other arm member toward the central portion,

a slot in the central portion adjacent said other end thereof,

the free end of the auxiliary spring arm being selectively tacts.

References Cited by the Examiner UNITED STATES PATENTS 1,225,758 5/17 Bristol et al. 200139 1,290,928 1/19 Denison 200-139 2,059,919 11/36 Teubner 200-4 2,891,128 6/59 Bolesky 200138 3,062,933 11/62 Burbey et al 200-438 BERNARD A. GILHEANY, Primary Examiner. 

1. A THERMALLY RESPONSIVE SWITCH COMPRISING, A SWITCH CASING, A MAINSPRING MOUNTED IN THE CASING, A MOVABLE CONTACT CARRIED BY THE MAINSPRING, A FIXED CONTACT IN THE CASING, A PAIR OF LEVERS PIVOTALLY MOUNTED IN SCISSORS FASHION ON THE MAINSPRING, ADJUSTMENT MEANS ON THE CASING, EACH OF THE LEVERS HAVING ONE END ROTATABLY ENGAGED WITH THE ADJUSTMENT MEANS, AND A THERMALLY RESPONSIVE MOVABLE ELEMENT CONNECTED WITH THE CASING, THE FREE ENDS OF THE LEVERS BEING POSITIONED IN THE PATH OF MOVEMENT OF THE THERMALLY RESPONSIVE ELEMENT FOR MOVING THE MOVABLE CONTACT INTO AND OUT OF ENGAGEMENT WITH THE FIXED CONTACT IN RESPONSE TO TEMPERATURE CHANGES. 